Use of Math.pow?

[Ogwal Boniface]

Hi techies,
Kindly help me the situation below:

//Interest.java
/*Mr. Brown invests $50,000.00 in a savings account yielding 5 percent interest. 
 * Assuming that all interest is left on deposit, write java codes to calculate and print 
 * the amount of money in the account at the end of each year for 10 years.
 * Use the following formula for determining these amounts:
 * a=P(1+r)n
 * Where:
 * P is the original amount invested i.e. the principal
 * r is the annual interest rate
 * n is the number of years
 * a is the amount on deposit at the end of the nth year
 * */

public class Interest {

	public static void main(String[] args) {
		double P=50000.00;
		double r=0.05;
		int n;
		for(n=1; n<=10; n++);
		
		System.out.println("The amount at the end of the first year is:" + P*(1+r)); 

/*this only prints the result for the first year and I would like to use this result
as the principal for the second year and the subsequent for the 3rd year and so on..**/

	}

}

Any help is appreciated
Thanks,
Bonny

[Ulf Dittmer]

Start by introducing the "a" variable. It needs to increase in each iteration.

[Henry Wong]

Not completely sure what you are asking... but why not? Sure, the Math.pow() method can be used here to raise the percentage to the number of years.

Henry

[Ogwal Boniface]

Hi,
I am particularly interested in the code that can make solve that problem based on the formula given and the scenario as a whole.

But Ulf, how can I introduce the 'a' variable to make the iteration?

Thanks

[Ulf Dittmer]

For starters, the loop needs to change. "for(n=1; n<=10; n++);" does nothing; instead, use something like

for (n=1; n<=10; n++) {
    // assign value to "a" according to the given formula,
    // then print out values of "n" and "a"
}

[Ogwal Boniface]

Hi Ulf,
Thanks alot for replying.
Your code:

for (n=1; n<=10; n++) {
    // assign value to "a" according to the given formula,
    // then print out values of "n" and "a"
}

What I did:

double a;
for (n=1; n<=10; n++) {
 a=P*(1+r);
System.out.println("The amount at the end of year" + n + is:" +a):
}

The output is: The amount at the end of year 11 is:52500.0
This amount is correct but why does it print year 11?
Also, how could I use this amount as the value of P for the second and so on till the 10th year?
I am a complete newbie in the Java world but please help.
Thanks alot

[Ulf Dittmer]

That code doesn't even compile; are you sure it's the code that you're running? If you fix the syntax errors to make it compile, then it will indeed run from 1 to 10 for n. What's still missing is that the formula for "a" isn't what's mentioned in the description (and hence doesn't change for higher "n").

[Priety Sharma]

[ UD: Thanks for your contribution, but we don't want to rob Ogwal of an opportunity to learn: JavaRanch is NotACodeMill ]

[Priety Sharma]

Ulf,

I realised it.
Thanks.

[Ogwal Boniface]

Hi Ulf & Priety,
Thanks for the comments. I have taken note.
Below is my refined code:

//Interest.java
/*Mr. Brown invests $50,000.00 in a savings account yielding 5 percent interest. 
 * Assuming that all interest is left on deposit, write java codes to calculate and print 
 * the amount of money in the account at the end of each year for 10 years.
 * Use the following formula for determining these amounts:
 * a=P(1+r)n
 * Where:
 * P is the original amount invested i.e. the principal
 * r is the annual interest rate
 * n is the number of years
 * a is the amount on deposit at the end of the nth year
 * */

public class Interest {

	public static void main(String[] args) {
		double P=50000.00;
	                double r=0.05;
                                double a;
		int n=1;
		a=P*Math.pow((1+r),n); // According to the given formula
	do{
	System.out.println("The amount at the end of the year" + n + "is:" +a);
                n++;           
                }
                while (n<=10);
	}

}

The ouput iterates ten times, incrementing 'n' but keeping same value of 'a'.
Kindly help me understand how I can increment 'n' first, before 'a' is calculated based on the formula.
Also, is there a way I could use the output when 'n=1' as the value of P when 'n=2' and so on till year 10?

**Priety**..I understand the meaning of JavaRanch is 'NotACodeMill http://faq.javaranch.com/java/NotACodeMill' but I am trying to come up atleast with something as per what I know so far...

Thanks again for the time. It's appreciated

[Ulf Dittmer]

You're calculating "a" only once - outside of the loop; you should move that statement into the loop.

[Ogwal Boniface]

Hi Ulf,
Thanks alot. It works.
But one more thing, is there a way I could use the output when 'n=1' as the value of P when 'n=2' and so on till year 10?
Whatever your believe is, remained blessed...
Regards,
Ogwal

[Priety Sharma]

Hi Ogwal,

Good that you have achieved what you were trying to do.

[Priety Sharma]

Hi Ogwal,

I have a doubt.

As far as I understand your requirement is like this:

Calculate the interest for 1 year on the beginning principal of 50000 using rate of interest as 5%.

Then for the 2nd year add the interest to the principal and recalculate the interest on it at 5% and so on for 10 years.

Is this right?


Then the calculation should show the following results:

The amount at the end of the 1 th year is:52500.0
The amount at the end of the 2 th year is:55125.0
The amount at the end of the 3 th year is:57881.2
The amount at the end of the 4 th year is:60775.3
The amount at the end of the 5 th year is:63814.0

When I ran your code the results were:

The amount at the end of the 1 th year is:52500.0
The amount at the end of the 2 th year is:57881.2
The amount at the end of the 3 th year is:67004.7
The amount at the end of the 4 th year is:81444.7
The amount at the end of the 5 th year is:103946.4

So is that code producing the right results?
Just curions.
Correct me if I am wrong.

[Campbell Ritchie]

It gave the correct results when I tried it. What are you doing differently?

[Ogwal Boniface]

Hi Prietty,
Below is my complete code and the subsequent output:

/*Mr. Brown invests $50,000.00 in a savings account yielding 5 percent interest. 
 * Assuming that all interest is left on deposit, write java codes to calculate and print 
 * the amount of money in the account at the end of each year for 10 years.
 * Use the following formula for determining these amounts:
 * a=P(1+r)n //this is(1+r)to power n
 * Where:
 * P is the original amount invested i.e. the principal
 * r is the annual interest rate
 * n is the number of years
 * a is the amount on deposit at the end of the nth year
 * */
public class Interest {

	public static void main(String[] args) {
		double P=50000.00;
		double r=0.05;
		double a;
		int n=1;
		do{
			a=P*Math.pow((1+r),n);
			System.out.println("The amount at the end of year" + n + "is:" +a);
			n++;
		}
while (n<=10);

	}
	
}
/*The Output is:
The amount at the end of year1is:52500.0
The amount at the end of year2is:55125.0
The amount at the end of year3is:57881.25000000001
The amount at the end of year4is:60775.312500000015
The amount at the end of year5is:63814.078125000015
The amount at the end of year6is:67004.78203125003
The amount at the end of year7is:70355.02113281253
The amount at the end of year8is:73872.77218945316
The amount at the end of year9is:77566.4107989258
The amount at the end of year10is:81444.73133887211
This is based entirely of the initial value of P and not the incremental ones based on the increasing number of years
*/

My main problem is to use like the value of year1 in the output as the value of P for the second year and so on, giving something as below:
year 1 is 52,500.00
year 2 is 57,881.25
year 3 is 67,004.78
year 4 is 81,444.73
year 5 is 103,946.41
year 6 is 139,298.13
year 7 is 196,006.46
year 8 is 289,590.81
year 9 is 449,250.39
year 10 is 731,781.55
Grateful for further assistance
Regards

[Priety Sharma]

Hi,

It gave the correct results when I tried it. What are you doing differently?

If its giving the correct results. Then its done.
If the formula mentioned in the spec. is just to be implemented in java.
I have no doubts then.
Thanks!